The present invention relates to a device for blowing and stretching a plastic parison for obtaining a container. The proposed device finds application in the sector of bottling with aseptic technology, for example in a moulding apparatus.
As it is known, in a bottling line using aseptic technology, controlling contamination is of primary importance for the containers to be filled, for the filling product and for the environments in which moulding and filling of the containers take place. In a bottling line using aseptic technology, it is indeed fundamental to ensure correct filtering of the gaseous fluids to be introduced into the controlled environment, correct management of the pressures in various zones so as to control the path of any undesirable particles, correct monitoring of the environment, and correct management and adequate quality of the C.I.P. (Cleaning-in-Place) and S.I.P. (Sterilization-in-Place) cycles. Control of environmental contamination in bottling plants was introduced at the beginning of the nineties with the adoption of “clean rooms”, i.e. contamination-controlled rooms inside which machines (e.g. blowing and filling machines) are installed.
A blowing machine supports blowing moulds which are made to open and close in order to receive parisons and mould the containers by blowing mid and high pressure air in parisons and by stretching them with a rod. The driving components of the moulds (i.e. rods, cams, rollers, actuators) have to be lubricated with oleous substances which results in accumulation, in proximity of the moulds themselves, of dirt and dust originated from wear. Therefore, the risks of environmental contamination are very high.
The current Applicant has recently developed a new moulding apparatus for a bottling line using aseptic technology. The new moulding apparatus comprises a moulding machine (i.e. a rotary carousel blowing machine), driving components for the machine and an isolation device suitable for defining a controlled-contamination environment for housing the machine. The carousel machine supports moulds of the “book” type, each constituted by two relatively movable half-portions and a bottom element cooperating with the half-portions in order to shape a bottom of the container. It must be pointed out that the driving components (including driving components specifically meant for the moulds) are located outside the controlled-contamination environment. In particular, the apparatus is equipped with tubular bodies, disposed partly inside and partly outside the environment, defining tubular cavities for the passage of the driving components. For example, rods for opening/closing the moulds rotate inside corresponding tubular bodies, thus causing the half-portions to move apart or to approach. On the other side, rods for raising/lowering the bottom element slide longitudinally inside corresponding tubular bodies in such a way as to allow the engagement/disengagement of the bottom element with the half-portions.
The new apparatus poses the necessity to develop a new device for blowing and stretching a plastic parison. Indeed, in prior art solutions, a blowing nozzle used to be applied to the mouth of the parison in order to inject mid and high pressure air (maximum 40 bar). Contemporaneously, a stretching rod used to be inserted into the parison from the mouth, the insertion of the stretching rod being guided by the blowing nozzle itself.
The main drawback of the prior art blowing and stretching solutions regard the fact that they are not suitable for being used in association with an isolation device. Indeed, the blowing nozzle actually constitutes a channel that, in case of application in the new apparatus, would link the controlled-contamination environment and the external (dirty) environment. Moreover, other solutions adopting elastic bellows in association with the stretching rod are not compatible with the sterilization issues concerning the stretching rod and the internal walls of the bellows. As a matter of fact, the pressure exerted by liquid and gaseous sterilizing substances would result in deformation of the bellows.
In this context, the technical task at the basis of the present invention is to provide a device for blowing and stretching a plastic parison for obtaining a container, which overcomes the drawbacks of the above-mentioned known art.